TECH SPOTLIGHT Etchants for ancient iron implements ously examined by J. Piaskowski, ex- I reagent. In contrast, Fig. 5 and 6 Jerzy Piaskowski hibited a structure with completely (100X and 500X) show only the ce- Janina Radzikowska* spheroidized cementite particles, mentite phase after etching with alka- Foundry Research Institute shown in Fig. 1 and 2 (100 and 500X). line sodium picrate reagent. Krakow, Poland However, in some blades spher- Some Damascus blades have been oidization was not complete, and made of hypoeutectoid steel. In one layers of cementite were found be- such blade discovered and examined olor etching by immersion has tween grains of tempered martensite. by B. Zschokke, an unevenly carbur- Cbeen the basic tool for revealing This was observed in Damascus ized structure was observed. It con- the microstructure of ancient and me- blades examined earlier by B. sisted of tempered martensite and dieval iron implements for many Zschokke, as shown in Fig. 3 and 4 small particles of cementite, and was years at the Foundry Research Insti- (100X and 500X). All of these micro- etched with Klemm’s I reagent as tute. The primary reagent is Klemm’s structures were revealed by Klemm’s shown in Fig. 7 (400X). It was also I, which tints ferrite grains blue to etched with alkaline sodium picrate brown as a function of their crystallo- reagent, as shown in Fig. 8 (400X). The graphic orientation, while carbides re- orange-blue-white pattern, which is main unaffected (white). Klemm’s I contains 100 mL of stock solution and 2 g of potassium pyro- sulfite (also called metabisulfite), K2S2O5. The stock solution is a satu- rated aqueous solution of sodium thio- sulfate, Na2S2O3. This etchant is also very helpful in revealing phosphorus segregation. The lowest phosphorus Fig. 1 — The microstructure of Damascus regions are colored blue. As the phos- sword blades made of hypereutectoidal steel phorus content increases, the color be- with completely coalesced cementite particles comes brighter, changing through after etching with Klemm’s I reagent (100X). yellow to white at the highest concen- Fig. 4 — The same microstructure as on tration. The classic alkaline sodium pi- Fig. 3, but magnified 500X. crate reagent differentiates cementite from ferrite; it colors cementite brown to black, while ferrite is unaffected. Its chemical composition is 25 g of sodium hydroxide (NaOH), 2 g of pi- cric acid (2,4,6-trinitrophenol), and 75 mL of distilled water, etching at 60 to 100°C (140 to 212°F). This article describes how these etchants have been used to analyze the microstructures of ancient iron im- Fig. 2 — The same microstructure as in Fig. plements, including Damascus steel 1, but magnified 500X. blades, Japanese swords, and bloom- Fig. 5 — The microstructure, as in Fig. 3, ery iron. but after etching with alkaline sodium picrate reagent (100X). Damascus blades The famous Damascus sword blades were usually made of hard, hypereutectoidal steel, forged and heat treated. Their structure is composed of particles of spheroidized hyper- eutectoidal cementite distributed between the grains of tempered martensite. Fig. 3 — The microstructure of Damascus Proof of the value of color etching sword blades made of hypereutectoidal steel was conducted on two blades of hard with layers of cementite between grains of tem- Damascus steel. The first one, previ- pered martensite, after etching in Klemm’s I Fig. 6 — The same microstructure as in Fig. *Member of ASM International reagent (100X). 5, magnified 500X. ADVANCED MATERIALS & PROCESSES/FEBRUARY 2001 45 visible in Fig. 9 (10X) and Fig. 10 (25X), the welding and forging process, the is due to phosphorus segregation and sword was heat treated; a fine acicular the forging process. (bainitic or martensitic) structure was observed at its cutting edge. Japanese swords Color etching with Klemm’s I The microstructures of early reagent permitted very exact recogni- Japanese swords reveal a very spe- tion of the technology of Japanese cialized and well-mastered tech- swords. Fig. 11 presents the micro- nology. The sword blade examined structure of the cross section of such a was characterized by the “makuri- blade (10X). The case-core interface kitaë” or “kofuse-kitaë” construction structure and surrounding region is type. H. Tanimura (1980) wrote that shown in Fig. 12 (100X) and Fig.13 this technology was common in the (500X). Fig. 7 — The microstructure of Damascus Shinto time period (1544 to 1880 A.D.), Some white layers of cementite blades made of hypoeutectoidal steel with small and it was found in the swords de- were observed at the grain bound- cementite particles, after etching with Klemm’s I reagent (500X). riving from the 19th century. aries. Klemm’s I reagent also revealed The core of such swords was made the phosphorous segregation in the of soft low-carbon steel, very suitable core material as well as enriched phos- for this purpose. This core was sur- phorous zones as halos surrounding rounded by high carbon steel. After the gray nonmetallic inclusions.

Fig. 8 — The same microstructure as in Fig.7 but after etching with alkaline sodium pi- crate reagent (400X). Fig. 11 — The microstructure of the cross section of a Japanese sword is clearly revealed after etching with Klemm’s I reagent (10X).

Fig. 9 — The orange-blue-white phosphorus segregation pattern in a Damascus blade made Fig. 12 — The case/core interface micro- Fig. 14 — The band microstructure of a of hypoeutectoidal steel after etching with structure of a Japanese sword after etching with spear head made of bloomery iron after etching Klemm’s I reagent (10X). Klemm’s I reagent (100X). with Klemm’s I reagent (25X).

Fig. 10 — The same microstructure as in Fig. 13 — The microstructure as in Fig. 12, Fig.15 — The same microstructure as in Fig. 9, magnified 25X. magnified 500X. Fig. 14, magnified 500X. 46 ADVANCED MATERIALS & PROCESSES/FEBRUARY 2001 Bloomery iron the alkaline sodium picrate reagent 5. “Du Damassé et des lames de Damas,” Klemm’s I reagent was very helpful permitted confirmation of the pre- by B. Zschokke: Revue de Metallurgie, Mé- for revealing the phosphorous segre- vious microstructure description, re- moires,Vol. 21, 1925, p. 635-669. gation in a spear-head from a barrow vealed by Klemm’s I etchant, and per- 6. “Metallographic Examination of a (ancient burial site) in Ausrijne mitted measurements of stereological Japanese Sword,” by J. Piaskowski: Journal of the Historical Metallurgy Society, Vol.27, Lithuania (Migration Time, fifth and features of this phase by color image No. 2, 1993, p.110-117. sixth centuries A.D.) forged of high- detection and segmentation. ■ phosphorus bloomery iron containing 0.39% P and 0.05% Cu. The characteristic “band structure” was the result of this elemental segre- For more information: Janina Radzi- gation, Fig. 14 (25X). White particles kowska, Foundry Research Institute, of hypereutectoid cementite were vis- Krakow, Poland; e-mail: jradz@iod. ible at higher magnification in the krakow.pl. layers with lower phosphorous con- Bibliography tent, Fig. 15 (500X). 1.Metallographic Instructions for Colour Klemm’s I reagent was very helpful Etching. Part I: Klemm Colour Etching,by E. in showing the extent of phosphorous Weck and E. Leistner: DVS GmbH-Düs- segregation, even when little was pre- seldorf, Vol 77, 1982. sent, as in Damascus steel. Also the 2. Reagents for Microstructure Tests of Iron shape and distribution of unetched Alloys, Polish Standard PN-61/H-04503, (white) cementite particles were PKN, Poland, 1961. clearly visible against the background 3. “Damascus Steel: The Greatest Achieve- of the colorful matrix. Bringing out the ments of Early Metallurgy,” by J. Pi- primary structure by revealing the askowski: Proceedings of First International Symposium for The History of Arabic Science, phosphorous segregation permitted How useful did you find the information Aleppo, Vol. 2, 1976, p. 238-245. presented in this article? determination of the forming dy- 4. “Metallographic Examinations of Two Very useful, Circle 270 namics of Damascene steel products Damascene Steel Blades,” by J. Piaskowski: Of general interest, Circle 271 and bloomery iron. J. for The History of Arabic Science,Vol. 2, Not useful, Circle 272 Tinting of cementite particles with 1978, p. 3-30.

Circle 20 or visit www.adinfo.cc 47